The invention relates to an improved kiln for heat treating slurries of material such as magnesite hydrate slurries.
In kilns which have been provided heretofore, overlying beds have been provided for the thermal treatment of materials, but in order to obtain adequate treatment, the kilns have been very tall requiring a great deal of space and requiring expensive construction. This type of construction has also required a high expenditure of thermal energy. In accordance with the concepts of the present invention, the height of the kiln chamber is greatly reduced, and the thermal energy and mechanical energy requirements are reduced with a commensurate improvement in operation and in the product obtained.
It is accordingly an object of the present invention to provide an improved thermal treatment kiln for the treatment of material such as magnesite hydrate wherein the operation is such that the required height of the kiln is reduced considerably over that which was necessary by methods heretofore practiced.
A further object of the invention is to provide a kiln construction which operates in accordance with a method that reduces the energy input required and insures trouble-free continuous operation with improved efficiency for an improved more consistent product.
In accordance with the principles of the invention, the structure embodies a kiln wherein the chamber therein has an upper portion and a lower portion. The upper portion is constructed as a spray chamber having nozzles arranged in the ceiling and/or the walls. The upper portion of the chamber provides a predrying or predehydrating chamber which prepares the material to such an extent that the material therein can be sintered or calcined in considerably fewer tiers of treatment than were heretofore required. The completion of calcining is done in the lower portion of the chamber wherein the material is passed through a series of tiers while continuing to be subjected to heated gases.
In accordance with the invention, the upper portion of the chamber has a centrally located gas vent outlet with the spray nozzles for spraying the slurry arranged circumferentially around the opening to spray the slurry downwardly. Heated gases are directed into the lower part of the upper chamber tangentially so that they ascend in a spiral path flowing countercurrent to the downwardly sprayed flow of slurry.
In accordance with the principles of the invention, a preferred arrangement provides that the height of the upper chamber, that is, the height from the uppermost tier of the lower chamber to the ceiling of the spray chamber is at least twice as great as the spacing between the tiers. By directing the gases tangentially into the upper chamber, the counterflow of gas engaging the downwardly sprayed slurry materials suspends them in their movement so as to prolong the predrying or preconditioning of the material and intensify this phase of the process.